Disease of Small Intestine

length of small intestine

3-9 meters

3 segments of small intestine

1. Duodenum

2. Jejunum

3. Ileum

length of duodenum

25-30 cm

________ is almost entirely retroperitoneal (located behind the peritoneum)

duodenum

Where does duodenum end?

Ligament of Treitz

dividing between upper and lower GI

Ligament of Treitz

what part of the small intestine is responsible for most of the absorption of nutrients?

Jejunum

What part of the small intestine is the distal 60%?

Ileum

What artery supplies the duodenum?

celiac artery

What artery supplies the jejunum?

superior mesenteric

What artery supplies the ileum?

superior mesenteric

What vein does the small intestine veins drain into?

portal vein

What are lacteals?

specialized lymph capillaries present in intestinal mucosa

-collect fat absorbed by the small intestine which has been packaged into chylomicrons

-intestinal lymph passes into the systemic circulation via the thoracic duct

Parasympathetic vs Sympathetic effects on digestion

parasympathetic = increase digestion

sympathetic = decrease digestion

The entire surface of the small intestine is covered by ___________________ _________

intestinal villi

What is the function of intestinal villi?

expand the absorptive surface area of the intestinal mucosa

What are lacteal vessels?

specialized ducts of the lymphatic system to carry fats

-closely associated with the nerves and blood vessels within the intestinal lining

-carry fats to the thoracic duct

Function of intestine

secretes, digests, absorbs

Major digestion organ

small intestine

The small intestine is responsible for ______% of fluid and electrolyte absorption

90%

Where does digestion begin?

mouth (saliva)

What is poorly digested in the human small intestine?

dietary fiber and many simple carbohydrates

Where does digestion of other complex biological molecules such as fats, nucleic acids and proteins?

intestinal lumen

-initiated by salivary lipase and amylase and gastric pepsin

Describe the pathophysiology of absorption in the small intestine

-due to osmotic forces with water moving freely across membranes

-when large macromolecules are digested into monomers, osmolality INCREASES, INCREASING the influx of water

-this fluid along with bile, pancreatic juice, gastric acid, and saliva are PASSIVELY ABSORBED

Osmolality ________ as the food moves through the digestive system

decreases

Most water soluble products of absorption flow into the _______ vein

portal vein

_______ are not water soluble

lipids

What are lipids packaged into?

chylomicrons

-they are large lipoproteins that are too large to enter capillaries so they pass into the lacteal vessels and are taken to systemic circulation via the thoracic duct

What are chylomicrons?

Chylomicrons are tiny fatty droplets composed of triglycerides, small amounts of phospholipids, cholesterol, free fatty acids, and some protein.

Lipids --> ________ --> ________ --> _________duct --> _________ vein --> heart --> systemic circulation

Lipids --> chylomicrons -->lacteal --> thoracic duct --> subclavian vein --> heart --> systemic circulation

Fed vs fasting state

Fed:

-controlled by food

-move bolus downstream

Fasting:

-motility is cyclic

-periodically clears accumulated mucus, food, bacteria

Digestion and absorption are facilitated by what type of contractions?

non-propulsive segmental contractions that mix the food (creates the bolus)

After the food is made into a bolus, it is moved on by what type of contractions?

propulsive peristaltic contractions

How far does the propulsive contractions allow the food to travel?

a few centimeters at a time

The circular muscle __________ distal to the bolus and __________proximally.

The longitudinal muscle _________ distally and _______ proximally.

Circular muscle:

RELAXES distally

CONTRACTS proximally

Longitudinal muscle:

CONTRACTS distally

RELAXES proximally

What is functional dyspepsia?

recurrent upper GI discomfort of unknown etiology

-pain centered in the upper abdomen, epigastric pain or burning, early satiety, or postprandial fullness

Does functional dyspepsia have heartburn?

no

Pyrosis = ?

heartburn

What can cause functional dyspepsia?

overeating

eating too quickly

high fat foods

stress or alcohol or coffee

Is there an obvious cause for symptoms for functional dyspepsia?

no

-symptoms are non-specific

-limited in usefulness for diagnosis

-physical exam is rarely helpful

Evaluation and treatment similar to other upper GI workups

antisecretory agents

abx if H. pylori

upper endoscopy if red flag symptoms

What is lactase?

enzyme that breaks down lactose into glucose and galactose

How does lactase change as we age?

high at birth but decline as we age

Lactase deficiency can be secondary to...

Crohn's disease

celiac sprue

viral gastroenteritis

giardiasis

short bowel syndrome

malnutrition

S/S of Lactase deficiency

bloating

abdominal cramps

flatulence

osmotic diarrhea

Treatment for Lactase deficiency

-patient comfort

-lower lactose intake

-calcium supplements (risk of osteoporosis)

-lactase enzyme replacement

What is celiac disease?

an autoimmune disease in which people cant eat gluten because is damages their small intestine

S/S of celiac disease

-can take 10 years to be diagnosed correctly

infants: diarrhea/steatorrhea, weight loss, abdominal distention, weakness, muscle wasting, growth retardation

adults: diarrhea, dyspepsia, depression, iron deficiency anemia, osteoporosis, short stature, delayed puberty, amenorrhea, and reduced fertility

"dermatitis herpetiformis" = ?

celiac disease

Recommended test for celiac disease

IgA tissue transglutaminase antibody (95% sensitive/specific)

Diagnosis of celiac disease is confirmed with...

biopsy of proximal and distal duodenum

Treatment of celiac disease

-removal of all gluten from the diet (wheat, rye, barley)

-refer to dietician

-may need dietary supplement for water soluble vitamins initially

Most common abdominal surgical emergency

appendicitis

most common age for appendicitis

10-30

Cause of appendicitis

obstruction of appendix by a fecalith, inflammation, foreign body, or neoplasm

When will gangrene and perforation develop in appendicitis?

within 36 hours

S/S of appendicitis

-periumbilical or epigastric pain with anorexia then moves to RLQ within 12 hours

-steady ache worsens with walking or coughing

-N/V

-low grade fever

-RLQ TTP

-+ rebound tenderness

-Psoas, obturator, Rovsing's signs (+)

Testing for appendicitis

-Leukocytosis (high WBC)

-abdominal ultrasound or CT scan

Complications of appendicitis

perforation

peritonitis

possible sepsis

Treatment of appendicitis

surgery

What is intussusception?

The telescoping of one part of the intestinal tract into another

most common bowel obstruction in pts under 2 years of age

intussusception

Most common cause of intussusception in children > 6 years old

lymphoma

Most common cause of intussusception in adults

carcinoma or adenoma

S/S of intussusception

-N/V, diarrhea

-COLICKY abdominal pain

-blood tinged stool (red currant jelly stools)

Treatment of intussusception

children = air or barium enema

adults = surgery

Ischemic Bowel Disease

Inadequate blood supply resulting in vascular compromise to bowel

-true abdominal EMERGENCY

Can the intestine survive infartion?

no

even if a small segment of bowel ischemia allows intestinal pathogens into the abdominal cavity which will lead to fatal sepsis

Describe how blood loss in IBD leads to sepsis/death

loss of blood supply/blood not being able to get out -> necrosis -> after 24 hours bacterial invasion making pt sepsis -> 3-4 days after perforation -> death

The typical claim of IBD is....

pain of ischemic bowel is OUT OF PROPORTION to physical findings

Types of IBD

-chronic mesenteric arterial occlusion

-acute mesenteric arterial occlusion

-venous occlusion

-nonocclusive arterial insufficiency

What causes chronic mesenteric arterial occlusion?

atherosclerotic plaques can cause occlusions of celiac, superior mesenteric and inferior mesenteric arteries

-if 1 of the 3 arteries remains patent there is no symptoms

If 1 of the 3 arteries remains patent in chronic mesenteric arterial occlusion are there symptoms?

no

Partial occlusion of the three vessel in chronic mesenteric arterial occlusion allows enough blood flow to supply the resting intesting, but can elicit what?

"intestinal angina" after eating

-if can function at rest, but when food eaten there is angina

Complete comprised of the three vessel in chronic mesenteric arterial can be caused by hypotension, hypovolemic shock or MI, which results in what?

decreased blood flow to intestine which results in ischemic disease

What is often the cause of acute mesenteric arterial occlusion?

-emboli from the heart (A-fib) or aorta or by rupture and thrombosis of an atherosclerotic plaque

Is it more likely for a proximal or distal acute mesenteric arterial occlusion more likely to be necrotic?

proximal = bowel may survive due to collateral circulation through arcades

more distal = probability of necrosis increases

What causes venous occlusion?

liver cirrhosis

pancreatitis

Higher venous pressure combined with pt who have a hypercoagulable process are at increased risk of ___________________

acute mesenteric vein thrombosis

The intestine normally receives about ____% of total cardiac output

20%

-after meals the arterioles dilate and the blood flow can double

What happens to arterials and the bowel in the presence of shock?

arterioles constrict -> increasing central pressure (blood goes to heart and brain) -> prolonged vasoconstriction leads to ischemic bowel disease (IBD)

-form of non occlusive arterial insufficiency

Testing for Ischemic bowel disease

1. supine and upright plain films initially

2. CT with IV and oral contrast

3. MRA

Treatment of ischemic bowel disease

multisystem support if sepsis (ICU)

anticoagulation (known thrombotic event)

vasodilators (early stages)

surgery

Mechanical obstruction

occurs when intestinal contents are prevented from moving forward due to an obstacle or barrier that blocks the lumen

-lumen of gut is occluded

Is mechanical obstruction a surgical emergency?

yes

two categories of mechanical obstructions

Simple or closed loop

simple vs closed loop mechanical obstruction

single = only at one point

closed loop = two points, trapped intestine contents/secretions

Two types of simple mechanical obstructions

1. adhesions

2. intussusception

most common cause of simple mechanical obstruction in adults

adhesions

Two types of closed loop obstruction

1. hernias

2. volvulus

most common cause of closed loop obstruction in adults

hernias

what is a volvus

intestine twisted itself into a knot

What is the cause of volvulus in children?

due to malrotation

in elderly, volvulus most typically affects what part of the colon?

cecum or sigmoid colon

Treatment of volvulus

sigmoidoscope may reduce the volvulus and allow colon to return to normal position

S/S of mechanical obstruction

-acute abdominal pain

-N/V

-pain is RHYTHMIC (associated with peristaltic waves)

-Pain is relieved by emesis

testing for obstructions (mechanical or functional)

1. plain abdominal films

upper GI with small bowel follow through

CT scan

Treatment of mechanical obstruction

surgery

-except childhood intussusception = air enema

treatment of childhood intussusception

air enema

Functional obstruction is more commonly known as ___

ileus